From WO2006/043866 (Atlas Copco Rock Drills AB) is previously known a valve controlled hydraulic percussive device which in principle works according to the following. When the percussive piston has performed a stroke, it is driven backwardly by hydraulic force supplied to a forward drive face. When the piston has moved a certain predetermined distance, the so called signal point is reached. A circumferentially extending groove in the percussive piston which has previously connected a high pressure channel with a signal conduit of a main valve at this point instead establishes a connection between the signal conduit and a draining conduit.
This result in that the spool of the main valve starts to switch and, as seen in the Figure in said document, move to the right, driven by a permanent, high pressure on the left driving surface of the valve spool. When the spool thereafter reaches a central position, the pressure thereby switches on the right side of the percussive piston from return pressure into high pressure, whereby the percussive piston is retarded in order to subsequently start a movement in the striking direction, to the left in the Figure of said document. When the groove in the piston again reaches the high pressure channel, the signal conduit on the main valve is again pressurized and the valve spool again starts to switch and thereby move to the left, as seen in the Figure.
The percussive device is dimensioned such that when the percussive piston hits the shank adapter, at the striking moment, the spool of the main valve has reached its central position and the high pressure on the right side of the percussive piston has again changed into return pressure (or low pressure), whereon a percussive cycle can be repeated.
This previously known percussive device works reliably and well, but has a limitation in theoretically reachable stroke frequency.